Here, But Functionally Gone

Extinction. The end of a species; no coming back. Many conservation efforts strive to save species from this fate, and a species’ risk of extinction can also be a major factor in determining its listing as endangered.

A recent study published in Nature suggests, though, that we may want to pay a bit more attention to something called “functional extinction” — the point at which a species has too few members to continue filling its ecological role, even though it may still have a way to go until traditional “numerical extinction.”

Researchers at Linköping University in Sweden ran a number of analytical models to determine how often and in what circumstances functional extinctions occur. They found that larger animals are more likely to become functionally extinct, often driving smaller animals in a food web to numerical distinction. What’s more, this functional extinction can occur following a population decline of as little as 30 percent, meaning that a species only has to lose a third of its members before other plants and animals in the same food web may start to disappear.

A decline in cougars in Zion National Park in the first part of the 20th century led to an increase in the mule deer population and subsequent threat to cottonwoods and other vegetation. Credit: Wayne Dumbleton.

The study is theoretical, relying on models rather than data and observation of any particular species. However, the authors note that this phenomenon has already been observed by other researchers in cases such as that of the sea otter. The health of the sea otter population correlates to the health of kelp forests, as sea otters keep the populations of sea urchins and others that feed on kelp in check. Since kelp forests can be an important carbon sink, declines in sea otter population can have wide ranging effects, indeed.

The study’s authors suggest that their results “lend strong support to arguments advocating a more community-oriented approach in conservation biology.” At American Forests, we strive to protect and restore ecosystems for the benefit of all of their inhabitants and maintain awareness of the state of keystone species upon whom the rest of an ecosystem depends. The whitebark pine in high elevations of the Greater Yellowstone Area, for example, is threatened by explosive populations of mountain pine beetle and other threats. Consequently, its ability to fulfill its ecological role is also compromised. As fewer whitebark pine seeds are produced, animals like grizzly bears and Clark’s nutcracker are feeling the loss. You can help us protect and restore ecosystems like these, for all of their inhabitants.